Conventionally, layered compounds such as LiCoO2, LiNi1/3Mn1/3CO1/3O2 and the like and spinel compounds such as LiMn2O4 and the like have been used as positive electrode materials (positive electrode active materials) of lithium ion secondary batteries. Even in the layered compounds, it is known that the compounds with high content of Ni such as LiNiO2 and the like show high capacitance. However, the lithium ion secondary batteries using the compounds with high content of Ni such as LiNiO2 and the like as described in Patent Document 1 or Patent Document 2 have a lower theoretical density compared with those using the compounds containing Co such as LiCoO2 and the like, and as a result, there is a disadvantage such that the energy density as a battery becomes low.
Hence, there is a method to improve electrode density by compounding treatment of attaching the conductive auxiliary agent on the surface of the positive electrode active materials, as described in Patent Document 3.
However, the compounding treatment is preformed by applying pressure and shearing force while mixing the positive electrode active material and the conductive auxiliary agent. Thus, if the force is too high, the technical problem such as leading to deterioration of the conductive auxiliary agent, worsening the rate discharge characteristic will exist.
Further, hereinafter, the lithium ion secondary battery is recorded as the ‘battery’ according to the circumstances.